Quantum cryptography could well be the first application of quantum mechanics at the individual quanta level. The very fast progress in both theory and experiments over the recent years are reviewed, with emphasis on open questions and technological issues.

Quantum Cryptography

We review the field of femtosecond pulse shaping, in which Fourier synthesis methods are used to generate nearly arbitrarily shaped ultrafast optical wave forms according to user specification. An emphasis is placed on programmable pulse shaping methods based on the use of spatial light modulators. After outlining the fundamental principles of pulse shaping, we then present a detailed discussion of pulse shaping using several different types of spatial light modulators. Finally, new research directions in pulse shaping, and applications of pulse shaping to optical communications, biomedical optical imaging, high power laser amplifiers, quantum control, and laser-electron beam interactions are reviewed.

Femtosecond pulse shaping using spatial light modulators

We describe devices in which optics and fluidics are used synergistically to synthesize novel functionalities. Fluidic replacement or modification leads to reconfigurable optical systems, whereas the implementation of optics through the microfluidic toolkit gives highly compact and integrated devices. We categorize optofluidics according to three broad categories of interactions: fluid–solid interfaces, purely fluidic interfaces and colloidal suspensions. We describe examples of optofluidic devices in each category.

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Developing optofluidic technology through the fusion of microfluidics and optics

Multiphoton interference reveals strictly nonclassical phenomena. Its applications range from fundamental tests of quantum mechanics to photonic quantum information processing, where a significant fraction of key experiments achieved so far comes from multiphoton state manipulation. The progress, both theoretical and experimental, of this rapidly advancing research is reviewed. The emphasis is given to the creation of photonic entanglement of various forms, tests of the completeness of quantum mechanics (in particular, violations of local realism), quantum information protocols for quantum communication (e.g., quantum teleportation, entanglement purification, and quantum repeater), and quantum computation with linear optics. The scope of the review is limited to ``few-photon'' phenomena involving measurements of discrete observables.

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Multiphoton entanglement and interferometry

Self-organized dendritic crystal growth is explored to assemble uniform semiconductor nanowires into highly ordered one-dimensional microscale arrays that resemble comb structures. The individual ZnO nanowires have uniform diameters ranging from 10 to 300 nm. They are evenly spaced on a stem with a regular periodicity of 0.1-2 micrometer. Under optical excitation, each individual ZnO nanowire serves as a Fabry-Perot optical cavity, and together they form a highly ordered nanowire ultraviolet laser array.

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Dendritic nanowire ultraviolet laser array.

We investigate the characteristics of a 37-channel micromachined membrane deformable mirror for wave-front generation. We demonstrate wave-front generation of the first 20 Zernike polynomial modes, using an iterative algorithm to adjust driving voltages. The results show that lower-order-mode wave fronts can be generated with good accuracy and large dynamic range, whereas the generation of higher-order modes is limited by the number of the actuator channels and the working range of the deformable mirror. The speed of wave-front generation can be as fast as several hundred hertz. Our results indicate that, in addition to generation of wave fronts with known aberrations, the characteristics of the micromachined membrane deformable mirror device can be useful in adaptive optics systems for compensating the first five orders of aberration.

Wave-front generation of Zernike polynomial modes with a micromachined membrane deformable mirror

Polarization-selective computer-generated holograms made with form-birefringent nanostructures were designed, fabricated, and evaluated experimentally at 1.5 µm. The fabricated element showed a large polarization contrast ratio (>250:1) and a high diffraction efficiency (>40% for a binary phase level element). The experimental evaluation was in good agreement with the design and modeling predictions.

Form-birefringent computer-generated holograms

A chromatic confocal microscope constructed with a white-light source in combination with a diffractive lens provides wavelength-to-depth coding for profile measurements of a three-dimensional sample. We acquired depth-section images nonmechanically and in parallel by incorporating a slit-scan confocal technique into the system. A system using a 100x objective obtained a depth resolution of 0.023 mum comparable with surface profilometers that operate using conventional confocal microscopy. Experimental measurements of a four-phase-level diffractive element and of a machined, metal bearing are presented.

Single-shot depth-section imaging through chromatic slit-scan confocal microscopy

We built and evaluated a hybrid electrical-packet/optical-circuit network for datacenters using a 10 μs optical circuit switch using wavelength-selective switches based on binary MEMs. This network has the potential to support large-scale, dynamic datacenter workloads.

A 10 µs hybrid optical-circuit/electrical-packet network for datacenters

A nonlinear optical processor that is capable of true real-time conversion of spatial-domain images to ultrafast time-domain optical waveforms is presented. The method is based on four-wave mixing between the optical waves of spectrally decomposed ultrashort pulses and spatially Fourier-transformed quasi-monochromatic images. To achieve efficient wave mixing at a femtosecond rate we utilize a cascaded second-order nonlinearity arrangement in a ?-barium borate crystal with type??II phase matching. We use this ultrafast technique to experimentally generate several complex-amplitude temporal waveforms, with efficiency as high as 10%, by virtue of the cascaded nonlinearity arrangement.

Pang-Chen Sun

Papers

Wave-front generation of Zernike polynomial modes with a micromachined membrane deformable mirror

Form-birefringent computer-generated holograms

Single-shot depth-section imaging through chromatic slit-scan confocal microscopy

A 10 µs hybrid optical-circuit/electrical-packet network for datacenters

Spatial temporal wave mixing for space time conversion.